1. Field of the Invention
This invention relates to a method of forming an electroconductive micro-pattern and also to a device having such an electroconductive micro-pattern. More particularly, it relates to a method of forming an electroconductive micro-pattern for an electronic circuit device having an ultramicro-structure and also to an electric device having such an electroconductive ultramicro-structure.
2. Related Background Art
Ultralarge scale integrated circuit devices including large-capacity random access memories and high speed CPUs have been developed in the course of the remarkable technological advancement in the field of semiconductors in recent years and they are currently taking an indispensable role in this modern society, which is often described as highly advanced telecommunication society. However, there still is an ever increasing demand for devices of the above identified category that have an greater capacity and/or provide a higher processing speed. Since the known technologies for producing and processing semiconductor materials cannot cope with such a demand, efforts have been paid to develop totally new technologies that can effectively be used to meet the demand.
Research efforts have been paid for electron devices operating on the basis of novel theories relating to the quantum effect that micro-structures in the order of nanometers can provide as such micro-structures are expected to take a vital role in the electronic technologies of the next generation. Micro-structures are so important for quantum effect electron devices and such a micro-structure is also referred to as a quantum dot or a quantum wire depending on the configuration and has a size of 100 nanometers, or substantially equal to the wavelength of an electron wave, or less. In particular, micro-structures less than 30 nanometers are required for devices that should operate properly at room temperature.
In an attempt to satisfy the above requirement, various micro-working processes involving the use of an electron beam lithography apparatus and/or a focused ion beam working apparatus have been proposed, although it is difficult to manufacture micro-patterns having a size less than 30 nanometers reliably with any of such processes on a high reproducibility basis.
Meanwhile, techniques have been proposed to draw a fine pattern by means of a scanning tunneling microscope (STM) adapted to observe an electroconductive minute object with a resolution less than a nanometer. For example, U.S. Pat. No. 4,785,189 discloses a low energy electron beam lithography apparatus comprising an STM construction. With the proposed apparatus, a probe having a sharp tip is brought close to a piece of electron beam-sensitive resist placed on an electroconductive thin film on a substrate in order to draw a pattern on the resist by irradiating a low energy electron beam.
Japanese Patent Application Laid-Open No. 6-119901 describes a micro-working process for directly processing an electroconductive specimen by means of an STM probe without using resist.
An atomic force microscope (AFM) makes it possible to observe an insulator specimen with a resolution less than a nanometer and micro-working processes utilizing an AFM have also been proposed (see inter alia, Japanese Patent Application Laid-Open Nos. 6-151392 and 6-291031). The AFM does not require the specimen to be electroconductive and hence can be used to process various insulator specimens including those made of resist. Thus, AFMs are expected to be used for a wide variety of applications.
Generally, as pointed out above, an electroconductive micro-structure having a size less than 30 nanometers has to be prepared on an insulator in order to realize a quantum effect electron device that operates properly at room temperatures. However, if the structure contains an insulating part therein, the micro-working process using an STM probe becomes inoperative there for detecting a tunnel current and hence for controlling the distance between the probe and the specimen. Then, as a result, the process will not proceed continuously and smoothly.
Of the above described processing techniques, those adapted for cutting a piece of resist placed on a substrate to form a resist pattern with the probe of an STM or an AFM and preparing a micro-structure on the substrate by means of a developing process or some other equivalent process using the resist pattern as mask can often experience a problem of a warped pattern during the developing process that results in an inability of producing a desired micro-structure.
In view of the above identified problems of the known technologies, it is therefore an object of the present invention to provide a method of forming a micro-pattern that is adapted to produce a micro-pattern on an insulating substrate on a high reproducibility basis. Another object of the invention is to provide an electric device operating as a quantum effect electron device having such a micro-pattern.
According to an aspect of the invention, the first object is achieved by providing a method of forming a micro-pattern comprising steps of:
forming an organic thin film on an insulating substrate;
processing said organic thin film by conducting a micro-cutting work on it, holding a probe in contact with said organic thin film by means of atomic force; and
producing an electroconductive thin film out of said organic thin film subjected to the cutting work by heating and baking it.
According to another aspect of the invention, the first object is also achieved by providing a method of forming a micro-pattern comprising steps of:
forming an organic thin film on an insulating substrate;
producing an electroconductive thin film out of said organic thin film by heating and baking it; and
processing said electroconductive thin film by conducting a micro-cutting work on it, holding a probe in contact with said electroconductive thin film by means of atomic force.
According to still another aspect of the invention, the second object is achieved by providing an electric device formed by means of either of the above methods of forming a micro-pattern.